LITHIUM-TRANSITION METAL COMPLEX COMPOUNDS HAVING Nth ORDER HIERARCHICAL STRUCTURE, METHOD OF PREPARING THE SAME AND LITHIUM BATTERY COMPRISING AN ELECTRODE COMPRISING THE SAME

ABSTRACT

A lithium-transition metal complex compound has an n th  order hierarchical structure in which n type structures represented by at least one unit of a th  order units in a range of 1×10-(a+5) m to 10×10-(a+5) m exist in a complex form, wherein n is a natural number that is 2 or greater, and a is a natural number in a range of 1 to 5. The lithium-transition metal complex may be prepared by heat-treating a mixture including a lithium source, a transition metal source, and solvent in contact with a natural material having a hierarchical structure. A lithium battery includes an electrode including the lithium-transition metal complex compound having the n th  order hierarchical structure. The lithium battery can have improved rapid charging characteristics, high power characteristics, and cycle characteristics.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. Ser. No.12/399,120, filed Mar. 6, 2009, now allowed, which claims the benefit ofKorean Patent Application Nos. 10-2008-0030782, filed on Apr. 2, 2008,and 10-2008-0096722, filed on Oct. 1, 2008, in the Korean IntellectualProperty Office, the disclosures of which are incorporated herein byreference.

BACKGROUND

1. Field

One or more embodiments relate to a lithium-transition metal complexcompound having an n^(th) order hierarchical structure, a method ofpreparing the same, and a lithium battery including an electrodecomprising the lithium-transition metal complex compound having an nthorder hierarchical structure. More particularly, one or more embodimentsrelate to a lithium-transition metal complex compound having an n^(th)order hierarchical structure, which is derived from a natural material,a method of preparing the same, and a lithium battery including anelectrode comprising the lithium-transition metal complex compoundhaving an n^(th) order hierarchical structure.

2. Description of the Related Art

Lithium ion batteries (LiBs) have been adopted as a power source of manyportable devices due to their high energy density and easy design.Recently, there has been a trend to use LiBs as a power source ofelectric tools, electric bicycles, and electric vehicles, in addition toportable IT devices, and thus research has been actively conducted on anactive material that has high power properties and can be chargedrapidly. In general, in LiBs, graphite having a high theoreticalcapacity and a low charge and discharge potential has been used as ananode active material. However, the charge and discharge potential ofgraphite is close to 0 V, and thus, an LiB using graphite cannot becharged at a rapid rate. In addition, when an LiB using graphite is toorapidly charged, Li metal may be extracted from an anode of the LiB.

To overcome these problems, lithium titanium oxides (Li₄Ti₅O₁₂ (LTO))have been proposed as a new anode active material. LTOs show a stableand reversible charge/discharge curve at a potential of 1.5 V withrespect to Li metal, and reach a theoretical capacity of 175 mAh/g.Moreover, the dimension of LTO is not changed by theintercalation/deintercalation of lithium ions, and thus LTO is referredto as a zero strain insertion material. In this regard, research hasbeen actively conducted on LTOs that can be used as an active materialthat provides batteries with rapid charging and high power.

To increase the charge and discharge rates of LTO, the mass diffusionrate should be increased. For this, if the LTO is in nano-sized units,the specific surface area of the LTO increases, and thus a larger amountof a binder is needed for forming an electrode. In this case, therelative content of the LTO active material in an electrode isdecreased, and thus the capacity of a battery including the electrodemay be decreased.

SUMMARY

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the invention.

To achieve the above and/or other aspects, one or more embodiments mayinclude a lithium-transition metal complex compound having an n^(th)order hierarchical structure in which n type structures represented byat least one unit of a^(th) order units in a range of 1×10^(−(a+5)) m to10×10^(−(a+5)) m exist in a complex form, wherein n is a natural numberthat is 2 or greater, and a is a natural number in a range of 1 to 5.

To achieve the above and/or other aspects, one or more embodiments mayinclude a method of preparing a lithium-transition metal complexcompound, the method including: providing a mixture including a lithiumsource, a transition metal source, and solvent; providing a naturalmaterial having a hierarchical structure as a template; and heattreating the mixture and the natural material while the mixture and thenatural material contact each other to obtain a lithium-transition metalcomplex compound having an n^(th) order hierarchical structure in whichn type structures represented by at least one unit of a^(th) order unitsin a range of 1×10^(−(a+5)) m to 10×10^(−(a) ⁺⁵⁾ m exist in a complexform, wherein n is a natural number that is 2 or greater, and a is anatural number in a range of 1 to 5.

To achieve the above and/or other aspects, one or more embodiments mayinclude a lithium battery comprising an anode, a cathode, and anelectrolytic solution, wherein at least one of the anode and the cathodecomprises the lithium-transition metal complex compound having an n^(th)order hierarchical structure as described above, or thelithium-transition metal complex compound having an nth orderhierarchical structure, prepared using the method as described above.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages will become apparent and morereadily appreciated from the following description of the embodiments,taken in conjunction with the accompanying drawings of which:

FIG. 1 is a scanning electron microscopic (SEM) image of a wing of amoth having a 3^(rd) order hierarchical structure;

FIG. 2 is a graph showing x-ray diffraction (XRD) data of Li₄Ti₅O₁₂ ofPreparation Examples 1 and 2 and Li₄Ti₅O₁₂ particles of ComparativePreparation Example 1;

FIG. 3A is a SEM image of carbonized cotton;

FIG. 3B is an image of Li₄Ti₅O₁₂ of Preparation Example 1 observed atthe same magnification as that of FIG. 3A;

FIG. 3C is a SEM image of the carbonized cotton of FIG. 3A at a greatermagnification;

FIG. 3D is a SEM image of Li₄Ti₅O₁₂ of Preparation Example 1 observed atthe same magnification as that of FIG. 3C;

FIGS. 4A and 4B are SEM images of Li₄Ti₅O₁₂ particles of ComparativePreparation Example 1;

FIG. 5 is a graph showing the rapid charging characteristics of thecells manufactured in Example 1 and Comparative Example 1;

FIG. 6 is a graph showing the high power characteristics of the cellsmanufactured in Example 1 and Comparative Example 1;

FIG. 7 is a graph showing the cycle characteristics of the cellsmanufactured in Example 1 and Comparative Example 1; and

FIG. 8 is a graph showing the high power characteristics of the cells ofExample 2 and Comparative Example 2.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to the like elements throughout. In this regard, thepresent embodiments may have different forms and should not be construedas being limited to the descriptions set forth herein. Accordingly, theembodiments are merely described below, by referring to the figures, toexplain aspects of the present description.

One or more embodiments include a lithium-transition metal complexcompound having an n^(th) order hierarchical structure in which n typestructures represented by at least one unit of a^(th) order units in arange of 1×10^(−(a+5)) m to 10×10^(−(a+5)) m exist in a complex form,wherein n is a natural number that is 2 or greater, and a is a naturalnumber in a range of 1 to 5.

The term “range of 1×10^(−(a+5)) m (meter) to 10×10^(−(a+5)) m (meter)”used herein refers to values between 1×10^(−(a+5)) m (meter) and10×10^(−(a+5)) m (meter), wherein the range includes the value of1×10^(−(a+5)) m (meter), but does not include the value of10×10^(−(a+5)) m (meter). Hereinafter, throughout the presentspecification including claims, the description of “range of1×10^(−(a+5)) m (meter) to 10×10^(−(a+5)) m (meter)” and all thedescriptions wherein a is substituted by a certain number should beunderstood based on the above description.

In addition, the term “a^(th) order units” used herein refers to therange of 1×10^(−(a+5)) m to 10×10^(−(a+5)) m that can be understood asdescribed above. For example, a 1^(st) order unit is in a range of1×10⁻⁶ m to 10×10⁻⁶ m. In this regard, a may be a natural number rangingfrom 1 to 5. Hereinafter, throughout the present specification includingclaims, the term “a^(th) order units” should be understood based on theabove description.

The lithium-transition metal complex compound having an n^(th) orderhierarchical structure will now be described in more detail withreference to FIG. 1, which is provided as an aid to explaining theconcept of an n^(th) order hierarchical structure. In particular, FIG. 1is a scanning electron microscopic (SEM) image of a wing of a mothhaving a 3^(rd) order hierarchical structure.

As shown in FIG. 1, the wing of the moth has three types of structuresin a complex form, that is, a channel (refer to A of FIG. 1), a pore(refer to B of FIG. 1), and a sub-channel (refer to C of FIG. 1).

In FIG. 1, the width of each of the protruding channels A of the mothwing of FIG. 1 is about 2 μm. Thus, a protruding channel A of the mothwing may be considered to be a 1^(st) order unit in the range of 1×10⁻⁸m to 10×10⁻⁸ m.

In FIG. 1, the pores B are formed on a surface of the protruding channelrepresented by A. The average diameter of the pores B is about 0.75 μm.Thus, a pore B on the protruding channel A of the moth wing may beconsidered to be a 2^(nd) order unit in a range of 1×10⁻⁷ m to 10×10⁻⁷m.

In FIG. 1, the sub-channels C are formed on a side surface of the poresB in each of the protruding channels A. The width of each of thesub-channels C is about 0.05 μm. Thus, a sub-channel C formed on a sidesurface of a pore B on a protruding channel A of the moth wing may beconsidered to be a 3^(rd) order unit in a range of 1×10⁻⁸ m to 10×10⁻⁸m.

In the moth wing shown in FIG. 1, the channels A represented by the1^(st) order unit, the pores B represented by the 2^(nd) order unit, andthe sub-channels C represented by the 3^(rd) order unit are not formedindependent of each other, but are formed on a surface of a structurerepresented by a higher order unit.

Based on this, the term “n type structures exist in a complex form” usedherein can be understood such that n type structures different from eachother do not exist individually, but co-exist such that a structurerepresented by a lower order unit is formed on a surface of or inside astructure represented by a higher order unit. Hereinafter, throughoutthe present specification including claims, the term “n type structuresexist in a complex form” should be understood based on the abovedescription. Herein, n may be a natural number that is 2 or greater.Herein, a specific material can be observed even to a molecular level,and thus the maximum value of n cannot be substantially defined.

The term “structures represented by at least one unit of a^(th) orderunits” used herein should be understood as a structure of which length,width, diameter, and the like can be represented by at least one unit ofa^(th) order units as defined above. Examples of such structures includewires, shapeless powder, sunk or protruding channels, shapeless pores,or the like. Hereinafter, throughout the present specification includingclaims, the term “structures represented by at least one unit of a^(th)order units” should be understood based on the above description.

The transition metal of the lithium-transition metal complex compoundhaving an n^(th) order hierarchical structure may be any transitionmetal suitable for use as an electrode active material of a lithiumbattery without particular limitation. Examples of the transition metalinclude at least one selected from the group consisting of Ti, Co, Ni,Al, Mn, V, Sn, Cr, Fe, Nb, Mo, Pd, Cd, In, Ge, W, Si, Sb, and Mg, butthe transition metal not limited thereto.

The lithium-transition metal complex compound may be represented by oneof the formulae selected from the group consisting ofLi_(1+δ)Fe_(1−x)M_(x)PO₄ where M is Mn, Ni, or Co, −0.1≦δ≦0.1, 0≦x≦1, anexample of a compound of this formula being LiFePO₄;Li_(1+δ)Ni_(x)Mn_(x)Co_(1−2x)O₂ where −0.1≦δ≦0.1 and 0≦x≦0.5;Li_(1+δ)Ni_(1−x−y)Co_(x)M_(y)O₂ where M is Al or Mg, −0.1≦δ≦0.1, 0≦x≦1,0≦y≦0.2, an example of a compound of this formula being LiCoO₂;Li_(1+x)Mn_(2−x)O₄ where 0≦x≦0.33, an example of a compound of thisformula being LiMn₂O₄; Li₄Ti₅O₁₂ (LTO); LiMnO₂; or LiNi_(0.5)Mn_(1.5)O₄,but the lithium-transition metal complex compound is not limitedthereto.

The n^(th) order hierarchical structure of the lithium-transition metalcomplex compound may be derived from a natural material.

The expression “the n^(th) order hierarchical structure of thelithium-transition metal complex compound may be derived from a naturalmaterial” used herein indicates that the lithium-transition metalcomplex compound has a hierarchical structure of the natural material,or further comprises another structure that can be represented by atleast one unit of a^(th) order units as described above, in addition tothe hierarchical structure of the natural material. For example,referring to FIG. 3D showing an image of Li₄Ti₅O₁₂ (LTO) prepared inPreparation Example 1, which will be described later, the LTO has wireand channel structures of a hierarchical structure of cotton as atemplate, and may also further have a pore structure that does not existin the hierarchical structure of cotton. Hereinafter, throughout thepresent specification including claims, the expression “the n^(th) orderhierarchical structure of the lithium-transition metal complex compoundmay be derived from a natural material” should be understood based onthe above description.

The natural material may be any material having a hierarchicalstructure, without particular limitation. Examples of the naturalmaterial may include cotton, paper, woven fabrics, wood, pollen, starch,sugar beet, grass, wings of insects, egg inner shell, hair, squid bones,bacteria, chitin, sea urchin, diatoms, and the like, but the naturalmaterial is not limited thereto.

According to an embodiment, the lithium-transition metal complexcompound may have a 3^(rd) order hierarchical structure in which thefollowing structures exist in a complex form: a shapeless particlestructure having a diameter represented by a 1^(st) order unit in therange of 1×10⁻⁶ m to 10×10⁻⁶ m; a channel structure having a widthrepresented by a 2^(nd) order unit in the range of 1×10⁻⁷ m to 10×10⁻⁷m, a 3^(rd) order unit in the range of 1×10⁻⁸ m to 10×10⁻⁸ m, or a4^(th) order unit in a range of 1×10⁻⁹ m to 10×10⁻⁹ m; and a shapelesspore structure having a lengthwise diameter represented by a 2^(nd)order unit in the range of 1×10⁻⁷ m to 10×10⁻⁷ m, a 3^(rd) order unit inthe range of 1×10⁻⁸ m to 10×10⁻⁸ m, or a 4^(th) order unit in the rangeof 1×10⁻⁹ m to 10×10⁻⁹ m.

The lithium-transition metal complex compound described above mayfurther comprise a carbonized natural material. The n^(th) orderhierarchical structure of the lithium-transition metal complex compoundmay be derived from the n^(th) order hierarchical structure of thenatural material. That is, the “natural material” may be a template usedin synthesizing the lithium-transition metal complex compound having ann^(th) order hierarchical structure. Examples of the natural materialmay include, as described above, cotton, paper, woven fabrics, wood,pollen, starch, sugar beet, grass, wings of insects, egg inner shell,hair, squid bones, bacteria, chitin, sea urchin, diatoms, and the like,but are not limited thereto.

The term “a carbonized natural material” used herein refers to acarbonaceous material obtained as a result of heat treating the naturalmaterial in an inert atmosphere. The heat treatment conditions used inthe preparation of the carbonized natural material may be conditionswhere the lithium-transition metal complex compound can be synthesizedfrom a mixture comprising a lithium source, a transition metal source,and a solvent. For example, the heat treatment may be performed underconditions, such as an inert atmosphere, a heating rate of 1° C./min to10° C./min, a final temperature of 300-1200° C., and a heat-treatingtime of 0.5-48 hours (for example, first heat treatment conditions thatwill be described later), but the conditions are not limited thereto.The heat treatment conditions used in the preparation of the carbonizednatural material may vary according to the types and amounts of thenatural material, lithium source and transition metal source used.

The carbonized natural material has an n^(th) order hierarchicalstructure in which n type structures represented by at least one unit ofa^(th) order units in a range of 1×10^(−(a+5)) m to 10×10^(−(a+5)) mexist in a complex form, wherein n is a natural number that is 2 orgreater, and a is a natural number in a range of 1 to 5.

More particularly, the carbonized natural material may have a 3^(rd)order hierarchical structure in which the following structures exist ina complex form: a shapeless particle structure having a diameterrepresented by a 1^(st) order unit in the range of 1×10⁻⁶ m to 10×10⁻⁶m; a channel structure having a width represented by a 2^(hd) order unitin the range of 1×10⁻⁷ m to 10×10⁻⁷ m, a 3^(rd) order unit in the rangeof 1×10⁻⁹ m to 10×10⁻⁹ m, or a 4^(th) order unit in a range of 1×10⁻⁹ mto 10×10⁻⁹ m; and a shapeless pore structure having a lengthwisediameter represented by a 2^(nd) order unit in the range of 1×10⁻⁷ m to10×10⁻⁷ m, a 3^(rd) order unit in the range of 1×10⁻⁸ m to 10×10⁻⁸ m, ora 4^(th) order unit in the range of 1×10⁻⁹ m to 10×10⁻⁹ m, but thestructure of the carbonized natural material is not limited thereto.

One or more embodiments include a method of preparing thelithium-transition metal complex compound having an n^(th) orderhierarchical structure as described above, the method including:preparing a mixture comprising a lithium source, a transition metalsource, and a solvent; preparing a natural material as a template; andheat treating the mixture and the natural material in contact with eachother to obtain a lithium-transition metal complex compound having ann^(th) order hierarchical structure in which n type structuresrepresented by at least one unit of a^(th) order units in the range of1×10^(−(a+5)) m to 10×10^(−(a+5)) m exist in a complex form, wherein nis a natural number that is 2 or greater, and a is a natural number inthe range of 1-10.

Examples of the lithium source may include conventional lithiumprecursors such as LiOH, CH₃COOLi, Li₂CO₃, LiCl, and the like. Examplesof the transition metal source may include M(R₁)_(r), M(Ha)_(q),M(NO₃)_(w), M(CH₃COO)_(z) (herein, M is selected from the groupconsisting of Ti, Co, Ni, Al, Mn, V, Sn, Cr, Fe, Nb, Mo, Pd, Cd, In, Ge,W, Si, Sb, and Mg, R₁ is a C₁-C₂₀ alkoxy group, Ha is a halogen atom,and r, q, w, and z are each independently 1, 2, 3, 4, or 5), and thelike. As specific examples, the transition metal source may beTi(iPrO)₄, Ti(OBu)₄, TiCl₄, Fe(NO₃)₃, Fe(CH₃COO)₂, FeC₂O₄, or FeCl₂, butthe transition metal source is not limited thereto.

The solvent may be a medium that facilitates the lithium source and thetransition metal source to react with each other as a result of heattreatment so as to form a lithium-transition metal complex compound. Thesolvent may be removed in the course of the heat treatment. Examples ofthe solvent may include conventional solvents such as water, alcohol(for example, methanol, ethanol, propanol, and the like), ketone (forexample, acetone, methyl-ethyl ketone), acetic acid, ether, ethylacetate, tetrahydrofuran, chloroform, dichloromethane, and the like, butthe solvent is not limited thereto.

Next, the natural material as described above is prepared as a template.The natural material has an n^(th) order hierarchical structure, and alithium-transition metal complex compound to which the n^(th) orderhierarchical structure of the natural material is transferred can beobtained. A lithium-transition metal complex compound comprising thecarbonized natural material can also be obtained, and the carbonizednatural material may also have the n^(th) order hierarchical structureof the natural material.

The contacting of the mixture comprising the lithium source, thetransition metal source, and solvent with the natural material is notparticularly limited, and may be performed using one of a plurality ofmethods such as immersion, spraying, or the like.

Next, the mixture comprising the lithium source, the transition metalsource, and solvent and the natural material are heat treated whilecontacting each other. In the heat treatment, the lithium source and thetransition metal source are used as a starting material, and synthesisof a lithium-transition metal complex compound having an n^(th) orderhierarchical structure derived from the natural material and carbonizingof the natural material may be performed and removal of the carbonizednatural material may be selectively performed.

The synthesis of the lithium-transition metal complex compound from thelithium source and the transition metal source, the transfer of thehierarchical structure of the natural material to the lithium-transitionmetal complex compound, and the removal of the natural material (in theremoval of the natural material, carbonizing of the natural material andthe removal of the carbonized natural material are simultaneouslyperformed) may be simultaneously performed in an air atmosphere at aheating rate of 0.1° C./min to 5° C./min (heating starts at roomtemperature) up to a final temperature of 300° C. to 1200° C. for aheat-treating time of 0.5 to 200 hours (including the heating time).However, such conditions may vary according to the lithium source,transition metal source and natural material used.

Alternatively, a first heat treatment process may be performed in whichthe synthesis of the lithium-transition metal complex compound from thelithium source and the transition metal source, and the transfer of thehierarchical structure of the natural material to the lithium-transitionmetal complex compound are performed, and the natural material iscarbonized to obtain a lithium-transition metal complex compoundcomprising the carbonized natural material. That is, as a result of thefirst heat treatment process, the lithium-transition metal complexcompound comprising the carbonized natural material can be obtained, andboth the carbonized natural material and the lithium-transition metalcomplex compound may have an original n^(th) order hierarchicalstructure of the natural material. The lithium-transition metal complexcompound comprising the carbonized natural material may be used in atleast one of an anode or a cathode of lithium batteries.

The first heat treatment process may be performed, for example, in aninert atmosphere at a heating rate of about 1° C./min to about 10°C./min (heating may start at room temperature) up to a final temperatureof about 300° C. to about 1200° C. for a heat-treating time of about 0.5to about 48 hours (including the heating time). However, such conditionsmay vary according to the lithium source, transition metal source andnatural material used. After the first heat treatment process, thenatural material is carbonized, and coexists with the lithium-transitionmetal complex compound. Thus, after the first heat treatment process,the lithium-transition metal complex compound comprising the carbonizednatural material, which is a template, can be obtained.

Subsequently, if it is desired that the carbonized natural material beremoved, a second heat treatment process in which the carbonized naturalmaterial is selectively removed may further be performed. As a result,the lithium-transition metal complex compound from which the carbonizednatural material is removed can be obtained. The second heat treatmentprocess may be performed, for example, in an air atmosphere at a heatingrate of about 0.5° C./min to about 5° C./min (heating starts at roomtemperature) up to a final temperature of about 300° C. to about 1000°C. for a heat-treating time of about 0.5 to about 48 hours (includingthe heating time). However, such conditions may vary according to thelithium source, transition metal source and natural material used.

The method of preparing the lithium-transition metal complex compoundhaving an n^(th) order hierarchical structure as described above ishighly reproductive and reliable, and uses as a template a naturalmaterial selected from natural materials having a variety ofhierarchical structures, so that a lithium-transition metal complexcompound having various hierarchical structures can be prepared.

The lithium-transition metal complex compound having an n^(th) orderhierarchical structure (including the lithium-transition metal complexcompound having an n^(th) order hierarchical structure comprising thecarbonized natural material having an n^(th) order hierarchicalstructure) and the lithium-transition metal complex compound having ann^(th) order hierarchical structure prepared using the preparationmethod as described above (including the lithium-transition metalcomplex compound having an n^(th) order hierarchical structurecomprising the carbonized natural material having an n^(th) orderhierarchical structure prepared by the first heat treatment process asdescribed above) have a structure in which the diffusion length oflithium ions is short and the total surface area thereof is relativelysmall, due to the n^(th) order hierarchical structure. Therefore, thelithium-transition metal complex compound having an n^(th) orderhierarchical structure can be used in at least one of an anode and acathode of secondary batteries, particularly, lithium batteries. In thisregard, the lithium-transition metal complex compound having an n^(th)order hierarchical structure comprising the carbonized natural materialhaving an n^(th) order hierarchical structure and the lithium-transitionmetal complex compound having an n^(th) order hierarchical structurecomprising the carbonized natural material having an n^(th) orderhierarchical structure prepared by the first heat treatment process asdescribed above further comprise a carbonaceous material, such as thecarbonized natural material, in addition to the lithium-transition metalcomplex compound. Thus, when they are used in lithium batteries,conductivity improvement due to the carbonized natural material can beobtained.

A lithium battery in which the lithium-transition metal complex compoundhaving an n^(th) order hierarchical structure or the lithium-transitionmetal complex compound having an n^(th) order hierarchical structurecomprising the carbonized natural material having an n^(th) orderhierarchical structure is used in a cathode can be manufactured asfollows.

First, the lithium-transition metal complex compound having an n^(th)order hierarchical structure or the lithium-transition metal complexcompound having an n^(th) order hierarchical structure prepared usingthe preparation method as described above as an active material, aconducting agent, a binder, and a solvent are mixed to prepare a cathodeactive material composition. Then, the cathode active materialcomposition is directly coated on an Al current collector and dried toprepare a cathode plate.

Next, an anode active material, a conducting agent, a binder, and asolvent are mixed to prepare an anode active material composition. Theanode active material composition is directly coated on a copper currentcollector and dried to prepare an anode plate. Alternatively, the anodeactive material composition may be cast on a separate support, and thena film formed of the anode active material delaminated from the supportmay be laminated on the copper current collector to prepare an anodeplate.

The solvent used in forming the active cathode material or the activeanode material may be any solvent that can be used in conventionalcompositions for forming an active material layer. Examples of thesolvent may include a chain-type carbonate, such as dimethyl carbonate,ethylmethyl carbonate, diethyl carbonate and dipropyl carbonate,dimethoxyethane, diethoxyethane, fatty acid ester derivatives, a cycliccarbonate, such as ethylene carbonate, propylene carbonate and butylenecarbonate, γ-butyrolactone, N-methylpyrrolidone, acetone, NMP, andwater. In this regard, one or a combination of at least two of the abovematerials may be used as the solvent.

The binder may be any known binder used to form an active materiallayer. Examples of the binder may include a vinylidenefluoride/hexafluoropropylene copolymer, polyvinylidene fluoride,polyacrylonitrile, polymethylmethacrylate, polytetrafluoroethylene,mixtures of these materials, and a styrene butadiene rubber polymer, butis not limited thereto. The amount of the binder may be within generalranges for forming an active material layer.

The anode active material may be any anode active material known in theart. Examples of the anode active material may include a metal-basedanode active material, a carbon-based anode active material, and acomposite anode active material thereof. The carbon-based anode activematerial may comprise at least one selected from the group consisting ofgraphite, natural graphite, artificial graphite, soft carbon and hardcarbon. The metal-based anode active material may comprise at least onemetal selected from the group consisting of Si, Sn, Al, Ge, Pb, Zn, Agand Au, or an alloy thereof. The composite anode active materialincluding both the carbon-based and metal-based anode active materialsmay be prepared by mixing the carbon-based anode active material and themetal-based anode active material by mechanical treatment such as ballmilling, or the like. If necessary, processes such as heat treatment,and the like may be further performed. The anode active material may bepreferably a Si/C composite anode active material or a Sn/C compositeanode active material. The conducting agent, the binder, and the solventin the anode active material composition are the same as those in thecathode active material composition. Here, the amounts of the anodeactive material, the conducting agent, the binder, and the solvent maybe amounts that are commonly used in a lithium battery.

Alternatively, an electrode formed of a Li metal can be used as an anodeplate. Various other modifications are also possible.

Any separator that is commonly used for lithium batteries can be used.In particular, the separator used may have low resistance to themigration of ions in an electrolyte and have an excellentelectrolyte-retaining ability. Examples of the separator include glassfiber, polyester, TEFLON, polyethylene, polypropylene,polytetrafluoroethylene (PTFE), a combination thereof. The material usedin the separator may be in non-woven or woven fabric form.

The separator is interposed between the cathode plate and the anodeplate to form an electrode assembly. The electrode assembly is wound orfolded and then sealed in a cylindrical or rectangular battery case.Then, an electrolytic solution is injected into the battery case tocomplete the manufacture of a lithium ion battery. Alternatively, aplurality of electrode assemblies may be stacked in a bi-cell structureand impregnated with an electrolytic solution. The resultant is put intoa pouch and hermetically sealed, thereby completing the manufacture of alithium ion polymer battery.

The electrolytic solution includes a lithium salt and a mixed organicsolvent of a high dielectric solvent and a low boiling point solvent,and if necessary, may further include a variety of additives such as anovercharge preventing agent.

The high dielectric solvent may be any high dielectric solvent that iscommonly used in the art without limitation. Examples of the highdielectric solvent include a cyclic carbonate such as ethylenecarbonate, propylene carbonate, and butylene carbonate, andγ-butyrolactone.

The low boiling point solvent may be any low boiling point solvent thatis commonly used in the art. Examples of the low boiling point solventinclude a chain-type carbonate such as dimethyl carbonate, ethylmethylcarbonate, diethyl carbonate (DEC), and dipropyl carbonate,dimethoxyethane, diethoxyethane, and fatty acid ester derivatives, butthe low boiling point solvent is not limited thereto.

At least one hydrogen atom existing in each of the high dielectricsolvent and the low boiling point solvent may be substituted with ahalogen atom such as fluorine.

The mixed volume ratio of the high dielectric solvent and the lowboiling point solvent may be in a range of about 1:1 to about 1:9. Whenthe mixed volume ratio is outside this range, discharging capacity andcharge-discharge cycles may be decreased.

In addition, the lithium salt used in the organic electrolytic solutionmay be any lithium salt that is commonly used in lithium batteries. Thelithium salt may comprise at least one compound selected from the groupconsisting of LiClO₄, LiCF₃SO₂, LiPF₆, LiN(CF₃SO₂)₂, LiBF₄,LiC(CF₃SO₂)₃, and LiN(C₂F₆SO₂)₂.

The concentration of the lithium salt of the organic electrolyticsolution may be in a range of about 0.5 to about 2 M. When theconcentration of the lithium salt is less than 0.5 M, the conductivityof the organic electrolytic solution may be decreased, and thus theperformance of the organic electrolytic solution may be poor. When theconcentration of the lithium salt is greater than 2.0 M, the viscosityof the organic electrolytic solution may be increased, and thus themobility of lithium ions may be decreased.

Exemplary embodiments will now be described in more detail withreference to the following examples. However, these examples are forillustrative purposes only and are not intended to limit the scope ofthe invention.

Example Preparation Example 1

0.38 g of LiOH and 5.3 g of Ti(iPrO)₄ were added to 6 g of EtOH, andthen the mixture was dissolved until it became transparent. Cotton(product name: Dong-A cotton, manufacturer: DONG-A HEALTHCARE) having asize of 4 cm×4 cm×0.5 mm was immersed in the mixture to permeate themixture into the cotton. The cotton with the mixture permeated thereintowas rolled, dried in a vacuum oven at room temperature, and put into acrucible. Then, the dried cotton was first heat treated at a heatingrate of 3° C./min up to a final temperature of 850° C. for 12 hours inan argon atmosphere to prepare Li₄Ti₅O₁₂ and to carbonize the cotton,thereby producing Li₄Ti₅O₁₂ comprising the carbonized cotton. Then, theresultant was secondarily heat treated at a heating rate of 2° C./min upto a final temperature of 450° C. for 12 hours in an air atmosphere toremove the carbonized cotton. As a result. Li₄Ti₅O₁₂ having ahierarchical structure of the cotton was obtained.

Preparation Example 2

4.25 g of Ti(OBu)₄ was dissolved in 1 g of EtOH. Separately, 1.07 g ofCH₃COOLi. 2H₂O was dissolved in 5 g of EtOH until the mixture becametransparent, and then the resulting solution was added dropwise to theprepared solution in which Ti(OBu)₄ was dissolved in EtOH. Then, filterpaper having a size of 11 cm×0.1 mm (product name: ADVANTEC,manufacturer: Toyo) was immersed in the mixed solution to permeate themixed solution into the filter paper. The filter paper with the mixedsolution permeated thereinto was rolled, dried in a vacuum oven at roomtemperature, and put into a crucible. Then, the dried filter paper wasfirst heat treated at a heating rate of 3° C./min up to a finaltemperature of 850° C. for 12 hours in an argon atmosphere to prepareLi₄Ti₅O₁₂ and to carbonize the filter paper, thereby producing Li₄Ti₅O₁₂comprising the carbonized filter paper. Then, the resultant wassecondarily heat treated at a heating rate of 2° C./min up to a finaltemperature of 450° C. for 12 hours in an air atmosphere to remove thecarbonized filter paper. As a result. Li₄Ti₅O₁₂ having a hierarchicalstructure of the filter paper was obtained.

Preparation Example 3

5.35 g of CH₃COOLi.2H₂O and 12.5 g of (CH₃COO)₂Co.4H₂O were added to 60g of H₂O, and then the mixture was dissolved until it becametransparent. Cotton (product name: Dong-A cotton, manufacturer: DONG-AHEALTHCARE) having a size of 4 cm×4 cm×0.5 mm was immersed in themixture to permeate the mixture into the cotton. The cotton with themixture permeated thereinto was rolled, dried in a vacuum oven at roomtemperature, and put into a crucible. Then, the dried cotton was firstheat treated at a heating rate of 3° C./min up to a final temperature of800° C. for 5 hours in an argon atmosphere to prepare LiCoO₂ and tocarbonize the cotton, thereby producing LiCoO₂ comprising the carbonizedcotton. Then, the resultant was secondarily heat treated at a heatingrate of 2° C./min up to a final temperature of 450° C. for 12 hours inan air atmosphere to remove the carbonized cotton. As a result. LiCoO₂having a hierarchical structure of the cotton was obtained.

Comparative Preparation Example 1

Commercially available Li₄Ti₅O₁₂ particles having average particlediameters in the range of about 0.3 μm to about 3 μm were obtained.

Comparative Preparation Example 2

Commercially available spherical LiCoO₂ particles each having an averageparticle diameter of about 20 μm were obtained.

Evaluation Example 1

The crystalline properties of Li₄Ti₅O₁₂ of Preparation Examples 1 and 2and Li_(a)Ti₅O₁₂ particles of Comparative Preparation Example 1 wereevaluated, and the results are shown in FIG. 2. The crystallineproperties were evaluated at about 40 mA and 40 kV using an X-raydiffraction (XRD) device known as X′Pert Pro available from Philips.

FIG. 2 is a graph showing XRD data of the Li₄Ti₅O₁₂ of PreparationExamples 1 and 2 and Li₄Ti₅O₁₂ particles of Comparative PreparationExample 1. Referring to FIG. 2, the Li₄Ti₅O₁₂ of Preparation Examples 1and 2 and the commercially available LiTi₅O₁₂ particles of ComparativePreparation Example 1 have peaks with a similar intensity ratio at thesame position. As a result, it can be seen that Li₄Ti₅O₁₂ wassynthesized in Preparation Examples 1 and 2, respectively.

Evaluation Example 2

To compare the hierarchical structure of the cotton used in PreparationExample 1 with the hierarchical structure of the Li₄Ti₅O₁₂ prepared inPreparation Example 1, the same type of cotton used in PreparationExample 1 was rolled, put into a crucible, and first heat treated at850° C. for 12 hours in an argon atmosphere to carbonize the cotton.Scanning electron microscopic (SEM) images of the carbonized cotton areshown in FIGS. 3A and 3C, respectively. For comparison, SEM images ofthe Li₄Ti₅O₁₂ of Preparation Example 1 are shown in FIGS. 3B and 3D,respectively, at the same magnifications as those of FIGS. 3A and 3C,respectively.

Referring to FIG. 3A, the cotton used as a template has a diameter ofabout 6.0 μm (for example, indicated by “a”). From this, it can be seenthat the cotton has a wire structure having a diameter represented by a1^(st) order unit in the range of 1×10⁻⁶ m to 10×10⁻⁶ m.

Referring to FIG. 3B, the Li₄Ti₅O₁₂ of Preparation Example 1 has adiameter of about 3.0 μm (for example, indicated by “b”). From this, itcan be seen that the Li₄Ti₅O₁₂ has a wire structure having a diameterrepresented by a 1^(st) order unit in the range of 1×10⁻⁶ m to 10×10⁻⁶m.

Referring to FIG. 3C, the cotton used as a template has a plurality ofchannels (portions represented by gray) recessed between ridges(portions represented by white lines). In FIG. 3C, it can be seen thatthe width (for example, indicated by “c”) of the channel can berepresented by a 2^(nd) order unit in the range of 1×10⁻⁷ m to 10×10⁻⁷m, a 3^(rd) order unit in the range of 1×10⁻⁸ m to 10×10⁻⁸ m, or a4^(th) order unit in the range of 1×10⁻⁹ m to 10×10⁻⁹ m.

Referring to FIG. 3D, the Li₄Ti₅O₁₂ of Preparation Example 1 has aplurality of channels (portions represented by gray) recessed betweenridges (portions represented by white line). In FIG. 3D, it can be seenthat the width (for example, indicated by “d”) of the channel can berepresented by a 2^(nd) order unit in the range of 1×10⁻⁷ m to 10×10⁻⁷m, a 3^(rd) order unit in the range of 1×10⁻⁸ m to 10×10⁻⁸ m, or a4^(th) order unit in the range of 1×10⁻⁹ m to 10×10⁻⁹ m. In addition,the Li₄Ti₅O₁₂ of Preparation Example 1 has shapeless pores (portionsrepresented by thick gray), and it can be seen that the lengthwisediameter (for example, indicated by “e₁”) of the pores can berepresented by a 2^(nd) order unit in the range of 1×10⁻⁷ m to 10×10⁻⁷m, a 3^(rd) order unit in the range of 1×10⁻⁸ m to 10×10⁻⁸ m, or a4^(th) order unit in the range of 1×10⁻⁹ m to 10×10⁻ ⁹ m.

From these results, it can be confirmed that the cotton used as atemplate has a 2^(nd) order hierarchical structure and that the 2^(nd)order hierarchical structure of the cotton is effectively transferred tothe Li₄Ti₅O₁₂ of Preparation Example 1. Moreover, the Li₄Ti₅O₁₂ ofPreparation Example 1 has a 3^(rd) order hierarchical structure byfurther having a pore structure as described above, in addition to the2^(nd) order hierarchical structure of the cotton.

FIGS. 4A and 4B are SEM images of the LiTi₅O₁₂ particles of ComparativePreparation Example 1, taken at the same magnifications as those ofFIGS. 3A and 3C, respectively. Referring to FIGS. 4A and 4B, theLi₄Ti₅O₁₂ particles of Comparative Preparation Example 1 are shapeless,and do not include a different structure having a size unit differentfrom the size unit of the Li₄Ti₅O₁₂ particle on a surface of theshapeless particles or inside the particles. Thus, it can be seen thatthe Li₄Ti₅O₁₂ particles of Comparative Preparation Example 1 do not havea hierarchical structure, unlike the Li₄Ti₅O₁₂ of Preparation Example 1.

Example 1

The Li₄Ti₅O₁₂ of Preparation Example 1 was pulverized to have an averageparticle diameter of about 2 μm. The pulverizing involved additionallypulverizing the Li₄Ti₅O₁₂ of Preparation Example 1, taking intoconsideration a size of an electrode. The Li₄Ti₅O₁₂ of PreparationExample 1 shown in FIG. 4B may be converted into shapeless particlesthrough the pulverization process, but the average particle diameterthereof is about 2 μm, and thus can still be represented by a 1^(st)order unit. The pulverized Li₄Ti₅O₁₂ of Preparation Example 1 was mixedwith SUPER P (a carbon black manufactured by MMM Carbon, Brussels,Belgium), and then a PVDF/NMP solution was added dropwise to the mixtureand stirred to prepare a slurry for manufacturing an electrode (theweight ratio of the Li₄Ti₅O₁₂ of Preparation Example 1:SUPER P:PVDF was82:10:8). The slurry was coated onto an Al substrate having a thicknessof about 15 μm by bar-coating, and then the resultant was dried underreduced pressure at a high temperature, rolled, and punched tomanufacture an electrode for a 2016 coin cell. The capacity of theelectrode was 2 mAh/cm², and the thickness thereof was about 90 to about100 μm.

The electrode manufactured as described above, an Li metal as a counterelectrode, and 1.3M LiPF₆ EC/DEC (3/7) as an electrolytic solution wereused to manufacture a half cell. To measure the capacity of the halfcell, charging and discharging were performed at a rate of 0.2 C. Toevaluate rapid charging characteristics, charging and discharging wereperformed at rates of 6 C and 0.5 C. respectively. To evaluate highpower characteristics, charging and discharging were performed at ratesof 0.5 C and 6 C, respectively.

Comparative Example 1

A cell was manufactured in the same manner as in Example 1, except thatLi₄Ti₅O₁₂ particles of Comparative Preparation Example 1 were usedinstead of the Li₄Ti₆O₁₂ of Preparation Example 1. Charging anddischarging were performed on the cell in the same manner as in Example1.

Example 2

The LiCoO₂ of Preparation Example 3 was pulverized to have an averageparticle diameter of about 2 μm. The pulverized LiCoO₂ of PreparationExample 3 was mixed with SUPER P, and then a PVDF/NMP solution was addeddropwise to the mixture and stirred to prepare a slurry formanufacturing an electrode (a weight ratio of LiCoO₂ of PreparationExample 3:SUPER P:PVDF is 96:2:2). The slurry was coated onto an Alsubstrate having a thickness of 15 μm by bar-coating, and then theresultant was dried under reduced pressure at a high temperature,rolled, and punched to manufacture an electrode for a 2016 coin cell.The capacity of the electrode was 3 mAh/cm², and the thickness thereofwas about 60 to about 70 μm.

The electrode manufactured as described above, an Li metal as a counterelectrode, and 1.3M LiPF₆ EC/DEC (3/7) as an electrolytic solution wereused to manufacture a half cell. To measure the capacity of the halfcell, charging and discharging were performed at a rate of 0.2 C. Toevaluate high power characteristics, charging and discharging wereperformed at rates of 0.5 C and 6 C, respectively.

Comparative Example 2

An electrode was manufactured in the same manner as in Example 2, exceptthat LiCoO₂ particles prepared in Comparative Preparation Example 2 wereused instead of LiCoO₂ of Preparation Example 3.

Evaluation Example 3

FIG. 5 shows curves when rapid charging was performed on cells ofExample 1 and Comparative Example 1 at a rate of 6 C. Referring to FIG.5, it can be seen that it takes about 59 minutes to charge 90% of therated capacity (standard charging rate of 0.2 C) of the cell ofComparative Example 1, while it takes about 21 minutes to charge 90% ofthe rated capacity (standard charging rate of 0.2 C) of the cell ofExample 1.

FIG. 6 is a graph showing high power characteristics of the cells ofExample 1 and Comparative Example 1. Referring to FIG. 6, it can be seenthat high power characteristics of the cell of Comparative Example 1 isabout 19%, while high power characteristics of the cell of Example 1 isabout 33%.

FIG. 7 is a graph showing cycle characteristics of the cells of Example1 and Comparative Example 1. To evaluate the cycle characteristicsthereof, each of the cells of Example 1 and Comparative Example 1 wascharged at a rate of 6 C and discharged at a rate of 0.5 C. and thecycle was repeated 50 times. Referring to FIG. 7, it can be confirmedthat after the cells were charged and discharged 50 times, the cell ofComparative Example 1 maintained about 31% of initial capacity, whilethe cell of Example 1 maintained about 92% of initial capacity.

FIG. 8 is a graph showing high power characteristics of the cells ofExample 2 and Comparative Example 2 when the cells are discharged at arate of 6 C. Referring to FIG. 8, the cell of Comparative Example 2exhibited about 62% of the rated energy density (standard dischargingrate of 0.2 C) at a discharging rate of 6 C, while the cell of Example 2exhibited about 22% of the rated energy density (standard dischargingrate of 0.2 C) at a discharging rate of 6 C.

As described above, according to the one or more of the aboveembodiments, when the lithium-transition metal complex compound havingan n^(th) order hierarchical structure, or the lithium-transition metalcomplex compound having an n^(th) order hierarchical structure preparedusing the method as described above is included in an electrode of alithium battery, rapid mass diffusion is possible. Thus, a lithiumbattery including the electrode can have improved rapid chargingcharacteristics, high power characteristics, and cycle characteristics.In addition, the method of preparing a lithium-transition metal complexcompound having an n^(th) order hierarchical structure uses a biotemplate such as a natural material, and thus the preparation method ishighly reproductive and reliable, and the manufacturing costs areinexpensive. Moreover the bio template has a variety of types, and thusa variety of n^(th) order hierarchical structures can be embodied.

Although a few embodiments have been shown and described, it would beappreciated by those skilled in the art that changes may be made inthese embodiment without departing from the principles and spirit of theinvention, the scope of which is defined in the claims and theirequivalents.

What is claimed is:
 1. A method of preparing a lithium-transition metalcomplex compound, the method comprising: providing a mixture comprisinga lithium source, a transition metal source, and solvent; providing anatural material having a hierarchical structure as a template; and heattreating the mixture and the natural material while the mixture and thenatural material contact each other to obtain a lithium-transition metalcomplex compound having an n^(th) order hierarchical structure in whichn type structures represented by at least one unit of a^(th) order unitsin the range of 1×10^(−(a+5)) m to 10×10^(−(a+5)) m exist in a complexform, wherein n is a natural number that is 2 or greater, and a is anatural number in a range of 1 to
 5. 2. The method of claim 1, whereinthe heat treating is performed at a heating rate of about 0.1° C./min toabout 5° C./min to a final temperature of about 300° C. to about 1200°C. for about 0.5 to about 200 hours in an air atmosphere.
 3. The methodof claim 1, wherein the heat treating comprises a first heat treatmentprocess in which a lithium-transition metal complex is synthesized andthe natural material is carbonized to form a lithium-transition metalcomplex compound comprising the carbonized natural material.
 4. Themethod of claim 1, wherein the first heat treatment process is performedat a heating rate of about 1° C./min to about 10° C./min to a finaltemperature of about 300° C. to about 1200° C. for about 0.5 to about 48hours in an inert atmosphere.
 5. The method of claim 3, after the firstheat treatment process, further comprising a second heat treatmentprocess in which the carbonized natural material is removed from thelithium-transition metal complex compound comprising the carbonizednatural material prepared by the first heat treatment process.
 6. Themethod of claim 5, wherein the second heat treatment process isperformed at a heating rate of about 0.5° C./min to about 5° C./min to afinal temperature of about 300° C. to about 1000° C. for about 0.5 toabout 48 hours in an air atmosphere.
 7. A lithium-transition metalcomplex compound prepared by the method of claim
 1. 8. A lithium batterycomprising an anode, a cathode, and an electrolytic solution, wherein atleast one of the anode and the cathode comprises the lithium-transitionmetal complex compound prepared by the method of claim 1.